Thanks Bill for this in-depth review. I'm very glad someone with considerably larger experience than me made the effort to test this zoom.

It's a great read which is recommended for every observer considering this eyepiece. And being bested only by the very best (Pentax XO5 and ZAOII 6mm) is not too bad for a barlowed zoom. Observing primarily the moon this review confirms my impressions of this zoom as an effective tool.

Nice report. I've been interested this eyepiece, and it's nice to here some critical observations.
Not being a planetary or lunar observer, I have a question.
How does one judge transmission differences that are likely in the neighborhood of 3-5 % when viewing a bright object like Mars? Sometimes I wonder if differences in contrast are confused with differences in light transmission. Bill. I'm not saying this is the case with your observations. You have much more experience than I do with such matters. I'm just wondering.

How does one judge transmission differences that are likely in the neighborhood of 3-5 % when viewing a bright object like Mars? Sometimes I wonder if differences in contrast are confused with differences in light transmission.

You are absolutely correct. It is difficult if not impossible to say with any assuredness if a perception is a result of transmission or contrast or even tonal differences. Only a bench test with measuring equipment could determine this. However, even a bench test won't necessarily mean that your perceptions will interpret them the same way. We've all seen the illustrations of how the huiman eye can be fooled into thinking something is brighter or a different color or a different shade when it actually is not. In my write up under Mars, I said: "Transmission and contrast appeared ...". I did not spell it out, but that is why I chose the word "appeared", simply to convey that this was the impression of the view between the two.

Your question also brings up a good point in what is really important in visual observational astronomy? Is it the actual behavior of things or the perceived behavior? IMO it adds nothing for me to know whether a point source or extended source is 3%-5% brighter or not. All that is important is if it appears brighter, larger, more detailed to my perception system. I often think we get too tied up around what is the actual factor that is happening if we were to do a bench test with measuring equipment. But in the end, since it is no guarantee that this is how one's perceptions may relay the truth of the matter, to me ALL that is important is how the perceptions react. So in the end, I think this is what makes great eyepieces great. Sure there is a portion of science in there with their transmission and contrast and tonal profiles, but what really makes them click is when the designers, by purpose or accident, get all the parameters just so so they knock it out of the park for our perception systems. So a great eyepieces needs some good science, but without the "art" of the design also it will just fall flat IMO.

At any rate, with the XO on Mars, the Pole looked nicely brighter, like those adds on TV for laundry detergents to choose which clothing looks whiter. It stood out more, gave the appearance of being actually brighter, while the surrounding dark features looked like they had more depth. So the XO was a 1/2 notch better in that regard.

thank you very much for this report! I have waited very long to see a test performed with a ~f/5 scope. Also, it's very nice to see a Brandon included in the test, even if it was outperformed. Now I "know", that the Leica ASPH would outperform my favourite planetary eyepieces, namely a 6mm Brandon and a barlowed 16mm Brandon (the Brandon which stayed at your and Jim Barnett's place before I received it). Should I ever buy the Leica (I think I will do in the near future), I would still keep my Brandons.